In many ophthalmic procedures, as for example cataract surgery, fluid under pressure is often supplied to the operative site to maintain a desired pressure in the eye. In recent years there have been a number of advances in cataract surgery techniques wherein instruments are inserted through the cornea of an eye to mascerate the lens material. Treatment fluid is supplied to the operative site through the surgical instrument and mascerated material and treatment fluid are withdrawn either through the surgical instrument or by an ancillary conduit.
In some cases the pressure of the treatment fluid delivered to the operative site is controlled simply by elevating or lowering a reservoir containing the treatment fluid. Obviously, this procedure cannot compensate for variations in pressure caused by changes in the rate of fluid flow or other conditions which vary the pressure.
In one cataract surgical procedure a computer is used to control pressure and also to monitor fluid flow rate so that surges will not cause a pressure rise great enough to damage the eye. Such apparatus is both complex and expensive.
Pressure regulators of the type utilizing a spring biased diaphragm are well-known. Such regulators are generally restricted to a limited range of flow rate and rapidly lose their regulating effect outside of that range.